Ultra-short wave directional coupler filter



April 26, 1960 cs. R. P. MARIE ULTRA-SHORT WAVE DIRECTIONAL COUPLER FILTER Filed Oct. 16, 1957 3 Sheets-Sheet 1 April 26, 1960 G. R. P. MARIE 3 Sheets-Sheet 2 April 26, 1960 G. R. P. MARIE 2,934,720

ULTRA-SHORT WAVE DIRECTIONAL COUPLER FILTER Filed Oct. 16, 195'? s Sheets-Sheet :5

United States ULTRA-SHORTWAVE DIRECTIONAL COUPLER FILTER- Georges Robert Pierre Mari, Paris, France Application October 16, 1957, Serial No. 690,514 Claims priority, application France November 19, 1956 i 12 Claims; cl. 333- first guide, the whole of the wave energy is transmitted to n i the second guide in the form of waves propagating in the opposite direction to that of the waves initially introduced, if in the first guide their frequency is comprised in the filters pass-band, while the energy continues to propagate in this first guide without being disturbed if their frequency is outside of the filters pass-band.

More precisely, the directional coupler filter according totthe invention is of the type in which 'two wave guides having rectangular cross-sections and parallel axes, and the crosssections of which have a common median plane parallel either to the longer sid'esof the cross-sections, of both guides or to the shorter sides of these cross-sections, are coupled through one or several resonant cavities by means of apertures provided in the side walls of these two guides facing each other;

The filter according to the invention is capable ofcoupling two rectangular cross-section wave guides in such a way that filtering takes place in the same'manner, whatever be the propagation direction considered in any one of these guides.

' respect to the, center of each one of the, said opposite walls and the dimensions of each one of the-said cavities, being chosen'in such a manner that it resonates for, a

metry plane of the said cavities parallel to their square, cross-section preferably passes through the axes of the said guides, the said coupling apertures being provided on two opposite walls of the cavity perpendicular to the said square cross-section and symmetrically arranged with predetermined-frequency located in the filter passe-band accordingtotwo;distinct oscillation modes TE and TE for which the indices p and q are respectively even and odd. t

According to a mode of embodiment of the invention, the two guides have equal cross-sections and'are coupled to the said cavity or cavities through their side walls. facing each other andcorresponding to one of the shorter,

sides of tl71eir v cross-section, and the length of the said cavity orcayities measured along their axis perpendicular to their square cross-section is at most equal to that of the said; shorter sides 3.

. According to another mode of embodiment of the invention, the coupling between the guides is provided by an assembly of several cavities with different resonance frequencies connected between the two guides and having eacl1 ;one-of their axes perpendicular to their, square .'cross-sectionszspaced from the nextone by an odd integer number of quarters of the phase wavelength in the guides for. a frequency equal to the average of the resonance frequencies of the said cavities,

' least :one' resonant cavitycoupling the said guidesds prot is made non-reciprocal.

' Directional coupler filters having similar properties are already known, for instance they have been described in the US. Patent 2,626,990 to I. R. Pierce. The filter according to, the invention improves over the known filters, in that it allows to obtain the same results with .a

smaller number of resonant cavities, thanks'to' the use of vided with a rodofferromagnetic material, the axis of whichsubstantiallycoincides with the axis of the said cavity perpendicular to'its square cross-section and the length'gof which is substantially equal 'to that of the said .cavi'tyi in the'dire'ctionlof'the latter axis, the transversal'dim'ensions of the said rod perpendicular to its axis being small with respect tothefside of the said square cross-section andthe'said rod being submitted to a constantv magnetic field parallel to its axis, whereby the filter According to :still another embodiment of the invention, a branching filter. is provided allowing the connecting of i a circular cross-section wave guide, propagating the TE i wave inone orthe other of its transmission directions,

, to a plurality of utilization devices, the said filter includis particularly well adapted to the use of such elements,

as the latter may be of a short length, which facilitates the application of the magnetic field by means of a perma nent magnet. t w

According to the present invention, a directional coupler filter is provided, comprising two rectangular cross-sec- 7 tion wave guides having parallel axes and the cross-sections of which have a common median plane parallel either to the longer sides or to the shorter sides of-both of these cross-sections, coupled, throughone or several resonant cavities of parallelepipedic' shape by means of the side length of the said crosssection, while the 'syming a first transitionelement. connecting the said circular guide to a main guide with a' rectangular cross-section and transforming the said TE wave into a TE wave in the said main guide, and a plurality of auxiliary guide lengths having, rectangular cross-sections and axes parallel 'to that of the said main guide and forming, together with the said main guide and corresponding resonant cavities, a plurality of directional coupler filters according to the inve'ntion, e ach one of *the latter, filters transmitting the ultra-high frequencywaves through a further transition 'member to a secondary rectangular cross-section connecteditofone" of the said utilization devices. 1 V

In ;the1,various above-mentioned embodiments of n the inventionithe resonant cavities may advantageously be provided 'with'movable plungers consisting of rods of dielectric material with.axesiperpendicularto the square cross-section, the position adjustment of' which allows to accurately adjust the resonance frequencies of these cavities. l I Y 'Besides, it results from the above-specified choice of the two oscillation modes of eachIof these cavities that their electric fields respectively have a symmetrical-configuration and an antisymmetrical configurationwith respect to' one or the other of the median planes of these cavitiesperpendicular to their square cross-section} f' I The invention will be better understood from the fol Patented Apr. 26, 1960' system of rectangular coordinates oxyz, in the case of waves'of the TE type propagating in the-guides.-

Figs. 2 and 3 represent two sections of the directional. coupler filter of Fig. 1 through plane Oxy. more pre cisely.

Fig. 2 represents a wave'system symmetricalwith're spect to the plane of geometric symmetry oyz, in a coupling cavity.

Fig. 3 represents a wave system antisymmetrical with.

respect to the same plane oyz, in'the same cavity.

Fig. 4 represents three cavities analogous to the cavity of Fig. 1 put in parallel connection between the two guides."

Fig. 5 shows the curve of the attenuation as a function of frequency, of the waves transmitted through a filter comprising the three cavities of Fig. 4.1 i

Fig. 6 represents a cavity similar to'that of Fig. 1 as to its dimensions, but coupling rectangular cross-section wave guides where TE waves propagate.

to the frequency of the incident waves, the energy which penetratesthrough openings 1 and 2 does not enter the cavity and issues symmetrically through the same openings. In the case of symmetrical energizing the exchange of energy between cavity 12 and guides 10 and 11 is eifectedalmost exclusively through the apertures 5 and 6 and not through the apertures-7 and 8. In fact, the

, latter are located in such regions where the electric field Fig. 7 represents an assembly of branching filters according to the invention, allowing the bidirectional operation of a circular cross-section guide propagating the TE wave and associated with several utilization devices,

either transmitters or receivers.

The; directional coupler filter represented in Fig. 1 is referred to a tri-rectangular axis system oxyz. The three coordinate planes of this coupler are three symmetry planes, if tuning devices which will be mentioned later on are neglected. The shorter sides ofguides 10 and 11 and the height of resonator 12 counted along oz are distinctly smaller than the half wavelength in free space of the waves which propagate in the considered assembly. It results therefrom that the electric-fields of these waves are constant along any straight line parallel to oz.

The device of Fig. 1 is built in such a way that a wave entering through section 1.of guide 10 issuesthrough section 3 of guide 11 if its frequency is equal .to the resonance frequency of cavity 12'. If not, the wave entering through opening 1 continues propagating in guide 10 and issues through section 2. The .wave motion is. easily analysed by considering. that the wave system existing in the said device results from the superposition of two'systems: the one symmetrical with respect. to the mechanical symmetry plane zoy, the other antisymmetrical with respect to this same plane z y. These two systems are represented in Figs. 2 and 3 by sectionsof the system through the plane xoy. The electricfield is everywhere perpendicular to the plane of the figure. The regions where the electric field is at a given. instant directed towards the positive direction of oz is shaded and the regions where the electric field is at the same instant directed towards the opposite direction of z are shown in blank.

' As an example, cavity 12 is supposed to oscillate according to the TE mode .and Figs. 2 and 3 show how the electric field for this mode is distributed in the cavity when the oscillation is symmetrical (Fig. 2) or antisymmetrical (Fig. 3) with respect to my. The straight lines which separate the shaded regions from those which are not, correspond in cavity 12 to planes where. the electric field is zero.

On Fig. 2, which is symmetrical with respect to plane is substantially zero and nocurrent circulates in the cavity walls in these regions.

As to the antisymmetrical oscillation represented in Fig. 3, here, to the contrary, the apertures 7 and 8 contribute to the exchange of energy between cavity 12 and guides 10 and 11, and not Sand 6. This is due to the face that for thisoscillation type, the apertures 5 and 6 are located in the neighbourhood of a zero electric field plane.

In the case of antisymmetrical oscillation (Fig, 3) and for waves of same amplitude entering in opposite phasethrough openings land 2, the energy issues anti-' symmetricallythrough 3 and 4, if the cavity 12 is tuned to their. frequency, or through land 2 if this is not the case.

If the two above-mentioned wave systems are superposed in such a way that the waves entering 2 are opposite in phase and cancel each other, the. issuing waves through 4 cancel each. other too; the energy exchange is then effected in the conditions already described. in connection with Fig. 1, provided, however, that the 'resonance frequencies andthe. loaded-Qs of the cavitybe the same for both. systems. For thecavity 12 a square cross-section is chosen, so that the. resonance frequencies corresponding to both of the oscillation modes be equal. In such conditions, the length ofthe sides of the square cross-section, when. the TE and TE modes. are used,

must be equalto the wavelength in free space. multiplied by' 13/2. 3 The resonance frequencies of the cavity arev adjusted byshifting the plungers 13 and 14 (Fig. 1),.

. metrically with respect to my the plungers 15 and 16.

towards the inside of the. cavity, the resonance frequency of the antisymmetrical oscillation mode with respect. to 1 y is likewise reduced without changing the-resonance frequency of the symmetrical mode.

On Fig. l where the cavity is shown from outside, the plungers 13 and 14, mechanically associated by a con.- necting member 20, may be seen; it is convenient to simultaneously handle the two plungers 13 and 14 in order to adjust the cavity resonance for the symmetrical oscillation mode with respect to zoy.

The two plungers 15 and 16 which allow adjustingof the antisymmetrical resonance are also mechanically associated by a member located on the other side of the device; therefore, they cannot be seen on Fig. 1.

If the resonances used are those according to the TE and TE modes; it is particularly easy to. adjust. the loaded-Qs of the cavity independently of each other for both of the considered modes. In fact, if thecoupling apertures 7 and 8 are located on both sides of 0y, at a distance vapproximately equal to a sixth of the length of the square side, they do not influence the loaded-Qv for the symmetrical oscillation mode with respect to 20).; thecoupling apertures such as Sand 6 located on the axis oyneither change the loaded-Q of the cavity for the antisymmetrical-resonance with. respect to the plane zoy. It is.v therefore possible to independently; adjust the loaded-Q for the symmetrical and. antisymmetrical modes with respect to zoy, by-respectiveadjustment of the 'size of the coupling apertures (5, 6) and (7, 8).

The coupling between guides 10 and 11 is of the type which reverses the direction of propagation of the waves; this is due,t the fact that, in the resonator 12, the spatial periodicity in the direction y is such that there is half a wavelength more for the antisymmetrical mode than for the symmetrical one.

,According to another embodiment of the invention, represented on Fig. 4, advantage is taken of the property of the coupling between guides andpll of reversing the direction of propagation of the waves, when passing from one guide to the other for the buildingof a filter with a wider pass-band, by parallel connection of several resonantrcavities tuned to different frequencies selected in thisbands The technical conditions to befulfilled for associating in parallel several resonant cavities jcoupling two guides with, parallel axes are explained in my co -pending patent application Serial No. 591,593, filed June 15, 1956. It is reminded that these conditions are the following:

(a) The coupling through the cavities must be, such' that it reverses the direction. of propagation of thewaves from one guide to the other.

(b) The axes of the cavities must be spaced by an odd number of quarters of the phase wavelength in the guides for, the average frequency of 'the transmitted band.

(0) The loaded-Qs of the cavities being assumed to" have a common value, the relative spacing of the resonance frequencies of two successive cavities must be-eq'ual to the reciprocal of this value.

In Fig. 4, three cavlties analogous to those represented several transmitters or destined for Several receivers propin Figs. 2 and 3, connected in parallel, are shown in' secj" tion. Fig. 5 represents, in dotted lines, three curves 21,- 22, 23 respectively giving for the three cavities 24, 25, 26 of Fig. 4 the attenuation A as a function of the frequency F of the waves, transmitted from input 27 to output 28 of the guides, supposing that only one cavity is -used, the'others having their coupling apertures shortcircuited. The curve 29 in full line shows theitransmis gear-rec course, be very near to the ferromagnetic resonancefrequencyof the material for the particular value of the constant magnetic field employed.

' The high frequency magnetic field to which the ferrite,

rected along 0y; and, if the two modes are superposed,

the two magnetic fields having the same amplitude and oscillating in phase quadrature add themselves vectorially. Depending on the fact that the rotating direction of the fieldis oris not the same as that of the natural precession of the magnetic intensity vector in the ferrite rod submitted to the constant magnetic field, the apparent'permeability of the ferrite rod will be very different, and the resonance frequency of the cavity will also be different. "There will be a resonance frequency for the waves entering 1 and issuing through? or entering 4 and issuing through 2 (these two wave systems just differing from one another by a rotation of 180 degrees around axis oz).

There will be another resonance frequency for the waves entering 3 and issuing through 1, or entering 2 and issuing through 4. p i

Still according to a further embodiment of the invention all previously described characteristics may be combjined in order to build branching filters allowing the use of a circular cross-section waveguide operating according' to theTE 'mode and in which waves generated by agate in both directionsii In my co-pending patent application Serial No. 620,029, filed October 22, 1956; a transition member is described, capable of transforming the TEM mode propagating in a circular cross-section guide into a TE mode propagating in a rectangular cross-section guide, as well as another transition member capable of transforming the TE mode propagating in a rectangular cross-section guide into a TE mode propagating in another rectangular cross-section guide.

The above-mentioned transition members will be respectively called' first and second type transition members.

Fig. 7 represents an assembly of branching filters which j-allows the bidirectional operation of a'cir'cular cross-section wave guide according to the TE mode by several transmitters and receivers. The circular guide section nearest to the filters is designated by 40 in Fig. 7,

while 41 is a; transition member of the first type which then be distinctly smaller than the half-wavelength'in free space of the transmitted waves. Thecoupling apertures must then be located on the broader side walls of the guides.

Except for the tuning devices, the device is mechanically symmetrical with respect to plane xoy. As in the case represented in Figs. 1, 2 and 3, the electric field is at any time antisymmetrical with respect to the mechanical symmetry plane xoy. If the guides 31 and 32 have their longer sides twice as long as those of guides Hand 11 (Figs. 1, 2 and 3) and'their shorter sides half as long as the latter ones, the currents in the neighbourhood of the coupling apertures are the same for both devices, if they receive the same electromagnetic energy. If all other dimensions are the same, the two considered devices have the same electrical characteristics.

- According to another embodiment of the invention, the coupling between guides 10 and 11 (Fig. 1) is made nonreciprocal by providing the cavity with a cylindrical rod of ferromagnetic material such as ferrite, directed along o'z; the ends of which rest on the inner square faces of the cavity and the diameter of which is small with respect to the side of said square faces. A magnet such as those represented in 51 and 52 (Fig. 7) creates a constant magnetic field in that rod. The wave frequencies should, of

transforms the TE wave of the circular guide into a TE wave in a rectangular guide. Threerectangular guide sections in which TE waves propagate and to which three filters according to the invention are con- I nected, are designated by 42, 43 and 44. Each one of these filters comprises two resonant cavities in parallel connection.

A Transition members of the second type 45 and 46 transformthe TE waves issuing from the filters 48 and 49 into TE waves in the rectangular guide, which propagate towards the receivers 53 and 54.

The filters 48 and 49 allow the passing of waves of relatively near frequencies which are {transmitted from the circular guide 40 to the receivers 53 and 54. 'The magnets 51 and 52 induce constant magnetic fields in cylindrical ferrite rods arranged along the axis of the cavities perpendicular to their square faces, thus making the filters 48 and 49 non-reciprocal. Failing this precaution, a TE wave emitted at the end 58 of the rectangular guide and having a frequency comprised in the pass-band of the receivers 53 and 54 would be directed towards the ends 56 and 57 of the wave guides, where suitable terminal irnpedances are provided. Owing to the fact that the filters are non-reciprocal, the cavities. of

filters 48 and 49 appear as distinctly out of tune for the waves issuing from 58,, which continue propagating to wards the circular, guide 49. It is therefore possible. to connect a transmitter 55 to the section 44 of the rectangular guide. The transition member 47 transforms the TE waves issued from 55. into TE' waves. The filter 50 directs these waves towards 44, then towards the circular guide 40. Owing to the fact that the filters 48 and 49 are non-reciprocal, the frequencies of the waves from 55 may be chosen in the frequency band of the waves received through 53 and 54, without disturbing the receivers.

The above examples are given for explanation purposes; they use the TE oscillation mode, but it is obvious that nothing is changedin the operating of the device when other TE modes are used, as indicated above. Within the scope of the invention, it is also possible to use a guide coupling arrangement comprising any number of apertures, for instance two, provided, however, that the loaded-Qs of the cavities be the same for the symmetrical and antisymmetrical oscillation modes. The adjustment of the loaded-Qs is made independently for the two modes in the above-described case, but the same adjustment of the loaded-Qs can experimentally be obtained for any number oi. apertures by successive trials.

What is claimed is:

1. An ultra-short wave four-port directional coupler band derivation filter, comprising first and second rectangular cross-section wave guide lengths having paral lel axes, a common median planeto their cross-sections passing through said axes and the longer and shorter sides of each one of said cross-sections respectively parallel to the longer and shorter sides of the otherof said cross-sections, a par-allelepipedic resonant cavity of square cross-section and having two opposite lateral walls perpendicular to said square cross-section respectively consisting of one and the other of the walls of said guides facing each other, said resonant cavity having a length perpendicular to said square cross-section much shorter than the side thereof, and an even number of coupling apertures arranged in each one of said lateral Walls symmetrically with respect to the center thereof, wherein the dimensions of said square cross-section are such that said cavity is capable of oscillating at a predetermined frequency in the derived band of said filter according to two distinct TE and TE modes, for which the values of integer numbers p and q are respectively even and odd, said four ports being constituted by openings at both ends of both said guide lengths.

2. A directional coupler filter as claimed in claim 1, wherein said guides have equal cross-sections and wherein said walls facing each other are those containing one shorter side of cross-sections of said guides.

3. A directional coupler filter as claimed in claim 1,.

wherein said guides have equal cross-sections and wherein said walls facing each other are those containing one longer side of the cross-sections of said guides.

4. A directional coupler filter as claimed in claim 1, wherein said cavity is provided with at least one pair of movable dielectric plungers symmetrically arranged with respect to one of its symmetry planes perpendicular to its square cross-section.

5. A directional coupler filter as claimed in claim 1, wherein the inside of said cavity is provided with at least one term-magnetic material rod having its axis perpendicular to its square cross-section, said filter funther including magnetizing means for impressing a constant magnetic field upon said rod in a direction substantially parallel to its axis.

6. An ultra-short wave four-port directional coupler band-derivation filter, comprising first and second rectangular cross-section wave guide lengths having parallelaxes, a common median plane to their cross-sections passing through said axes and the longer and shorter parallel to the longer and shorter sides of the other ofsaidcross-sections, a plurality of parallelepipedic resonant cavities of square cross-sections, each. having two lateral walls perpendicular to its said square cross-section respectively consisting of one and the other of the walls of said guides facing each other, said resonant cavities having a length perpendicular to their square cross-section much shorter than the side thereof, and an even number of coupling apertures arranged in each one of said lateralwalls symmetrically with respect to the center thereof, wherein the dimensions of the cross-section of each one of said cavities are such that said cavity is capable of oscillating at a predetermined frequency in the derived band of said filter according .to two distinct TEg, and TE modes, for which the values of the integer numbers p and q are respectively even and odd, and wherein the distance between the centers of two successive of said cavities is substantially equal to an odd number of quarter phase wavelengths in said guides at the mean irequ'ency of the said derived band of said filter, said four ports being constituted by openings at both ends of both said guide lengths.

7. A directional coupler filter as claimed in claim 6, wherein said guides have equal cross-sections and wherein said'walls facing each other are those containing one wherein at least one of said cavities is provided with at least one pair of movable dielectric plungers symmetri-' cally arranged with respect to one of its symmetry planesperpendicularto its square cross-section.

10. A directional coupler filter. as claimed in claim 6, wherein the inside or" at least one of said cavities is provided with at least one ferromagnetic material rod having its axis perpendicular to its square cross-section, said filter further including magnetizing means for impressing a constant magnetic field upon said rod in a direction substantially parallel to its axis.

ll. A 'multidirectional branching filter for ultra-short waves comprising a length of circular cross-section wave guide, a first transition member connecting said circular guide to a main rectangular cross-section wave guide, a plurality of auxiliary rectangular cross-section wave guides having their axes parallel tothe axis of said main guide, resonant cavities of parallelepipedic shape and square cross-sections each having two opposite lateralwalls perpendicular to its square cross-section respectively cosisting of one wall. of said main guide and of. one wall. of one of said' auxiliary guides facing each" other, an even number of coupling apertures arranged in each one of said lateral Walls symmetrically with respectjtothe center thereof, a plurality'of further transition members each one of which connects one of said auxiliary guides to one corresponding secondary guide, and means. for connectingeach one of 'said secondary guides to a utilization device, wherein the dimensions of the crossquency according to two distinct TE and TE modes,-

for which the values of the integer numbers p and q are respectively even and odd.

12. A multidirectional branching filter as claimed in claim 11, wherein the inside of at least one otsaid cavities is. provided with at least one ferromagnetic. material. rod having its axis perpendicular to the square crosssection of said cavity, said filter further including mag-- netizing means for impressing a constant magnetic field upon said rod in a direction substantially parallel to its:

axis.

(References on foliowing page) References Cited in the file of this patent OTHER REFERENCES UNITED STATES PATENTS Reich et aL: Microwave Theory and Techniques, 2,626,990 Pierce Jan. 27, 1953 copyright 1953 by D. Van Nostrand Company, Inc. pages 2,748,350w Miller May 29, 1956 5 482-486 relied upon. 7 2,823,356 Miller Feb. 11, 1958 FOREIGN PATENTS 64.770 France Jime 29, 1955 (First addition to 1,079,880) 

